YEREVAN — Armenian Prime Minister Serzh Sarksyan said he was resigning on Monday to help maintain civic peace following almost two weeks of mass street protests that have plunged the impoverished ex-Soviet republic into political crisis. Sarksyan, a close ally of Russian President Vladimir Putin, had served as Armenia’s president for a decade until this month and had faced accusations of clinging to power when parliament elected him as prime minister last week. Under a revised constitution, the prime minister now holds most power in the tiny southern Caucasus nation, while the presidency has become largely ceremonial. Pressure on the 63-year-old to quit had increased sharply on Monday when unarmed soldiers in the capital Yerevan joined the anti-government protests which first began on April 13. Though peaceful, the tumult has threatened to destabilize Armenia, a key Russian ally in a volatile region riven by its decades-long low-level conflict with Azerbaijan. Moscow, which has two military bases in Armenia, was closely watching events. “I got it wrong,” Sarksyan said in a statement issued by his office. “In the current situation there are several solutions, but I won’t choose any of them. It’s not my >